Thanks, all. We have two clowns, a starry blenny, flame back angel, and two damsels (Talbot and springer). The flame back angel has shown some dominance over the tomini, but hasn't done anything overly aggressive that I've seen.
The tomini does hang out under a rock overhang and often darts around the rocks. I'm guessing this may be what caused the marking, but will monitor over the next couple of days and course correct if needed.
Thanks again for all the help!